Graeme McDowell has withdrawn from the Texas Open after nine holes with a left ankle injury.
The 2010 U.S. Open winner from Northern Ireland told PGA Tour officials that his ankle had been giving him trouble for the past few weeks.
Jimmy Walker opened a four-stroke lead over fellow Texan Jordan Spieth, shooting a 3-under 69 on Saturday in his hometown Texas Open.
Walker, who lives 35 minutes away from TPC San Antonio, is looking for his fifth title in two tour seasons. He had a 9-under 207 total after opening with rounds of 71 and 67.
Jimmy Walker made himself right at home on the Texas Open leaderboard.
Walker won his hometown event Sunday to become the first two-time winner this season on the PGA Tour, beating fellow Texan Jordan Spieth by four strokes.
"(Spieth) really made me fight hard," Walker said. "He kept hitting it close, and I had to keep making putts."